1. Field of the Invention
This invention relates to an image reading device, method and program for reading an image of a transparent document such as a photographic film.
2. Description of Related Art
A photograph is taken under various environments of the natural world. Therefore, there are various kinds of images to be recorded to a transparent document such as a photographic film, ranging from those whose range from the brightest point to the darkest point is wide to those whose range from the brightest point to the darkest point is narrow.
Because of this, when an image that has been actually recorded on a photographic film (e.g., a negative film) is read by a film scanner, prescanning is performed prior to main scanning.
The darkest point and the brightest point of the image can be pre-detected by this prescanning. Additionally, during main scanning, based on the darkest and brightest points of the image that have been detected by this prescanning, image reading conditions are determined, such as exposure amount (exposure time) when image data is read and LUT (Look Up Table) gradation conversion characteristics.
However, when foreign matter such as dust is attached to the film surface, or when there is a scratch, etc., this can be considered as an image during prescanning. This causes problems, particularly in the case of a transparent document such as a negative film. That is, foreign matter such as dust usually shields visible light and deteriorates a visible component level of image data. Because of this, an image of foreign matter may be determined to be the darkest point (the lowest point of the range) of an image (negative image) that has been recorded on the film. Thus, when the darkest point is erroneously recognized, the most appropriate value cannot be obtained for the exposure amount (exposure time), for the LUT gradation conversion characteristic, or the like, when the image is read during main scanning.
The same can be said for the case in which there is a scratch on a photographic film.